Non-lubricating fluid pumping system

ABSTRACT

One or more techniques and/or systems are disclosed for a pump technology that provides for more effective and efficient transfer of liquids, such as glycol products, in a glycol dehydration system. Such a technology can comprise a type of external gear pump that can effectively handle harsh conditions associated with glycol dehydration system at high pressures, while providing for longer pump life, effective operations at higher temperatures, and operations that account for thermal shock; with improved sealing capability, in a cost-effective system. An example pump may comprise hardened internal components, improved clearances, a jacket to mitigate thermal shock, and/or a thermal shock plate to mitigate thermal shock.

RELATED APPLICATION DATA

This application claims benefit of U.S. Provisional Application No.62/727,088 filed Sep. 5, 2018, which is incorporated herein byreference.

BACKGROUND

Extracted natural gas is typically saturated with water, such as watervapor, particularly when extracted from an underground source. Beforebeing commercially marketed, the water is removed from the natural gasusing a dehydration process. Commonly, glycol products are used in thedehydration process. Glycol is a liquid desiccant used in a glycoldehydration system for the removal of water from natural gas (NG) andnatural gas liquids (NGL). Common types of glycols used includetriethylene glycol (TEG), diethylene glycol (DEG), ethylene glycol(MEG), and tetraethylene glycol (TREG). A glycol dehydration system canuse a pump for pumping the glycol through the system. Such pumps aresubjected to operational conditions that often lead to short pump life,sensitivity to thermal shock, temperature limits of existing pumps, andleakage issues.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key factors oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

One or more techniques and systems are described herein for a pumptechnology that provides for more effective and efficient transfer ofliquids, such as glycol products, in a glycol dehydration system. Such atechnology can comprise a type of external gear pump that caneffectively handle harsh conditions associated with glycol dehydrationsystem at high pressures, while providing for longer pump life,effective operations at higher temperatures, and operations that accountfor thermal shock; with improved sealing capability, in a cost-effectivesystem. In one implementation, a pump for pumping non-lubricating fluidsat elevated temperatures may comprise an internal pump chambercomprising a first material. Further, the pump may comprise a drivershaft that provides rotational power to the pump; and a driven shaftthat rotates as a result of the rotational power from the driver shaft.Additionally, the example, pump can comprise a first external geardisposed on the driver shaft in the internal pump chamber; and a secondexternal gear disposed on the driven shaft in the internal pump chamber.The first external gear and the second external gear may comprise asecond material, different than the first material. The first gear andsecond gear may be disposed in an intermeshing engagement that drivesfluid through the internal pump chamber under the rotational power. Theexample pump may also comprise a head assembly disposed an end of thefirst shaft and second shaft. The first material and the second materialmay be rated to 350° F. and may be resistant to thermal shock.

To the accomplishment of the foregoing and related ends, the followingdescription and annexed drawings set forth certain illustrative aspectsand implementations. These are indicative of but a few of the variousways in which one or more aspects may be employed. Other aspects,advantages and novel features of the disclosure will become apparentfrom the following detailed description when considered in conjunctionwith the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are component diagram illustrating oneimplementation of an example pump for pumping glycol.

FIGS. 2A, 2B, and 2C are component diagram illustrating anotherimplementation of an example pump.

FIGS. 3A, 3B, and 3C are component diagram illustrating anotherimplementation of an example pump.

FIGS. 4A, 4B, and 4C are component diagram illustrating anotherimplementation of an example pump.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are generally used to refer tolike elements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the claimed subject matter. It may beevident, however, that the claimed subject matter may be practicedwithout these specific details. In other instances, structures anddevices are shown in block diagram form in order to facilitatedescribing the claimed subject matter.

Pumping glycol in a glycol dehydration system for natural gas has threecommon challenges: high temperature operation (e.g., can beapproximately 200 Deg. F, or from about 175 to 225 Deg. F, but typicallyfrom about 140-160 Deg. F), at high pressures (e.g., up to 1500 psi),with a low lubricity liquid (e.g., glycol), with the potential forabrasives (e.g., sand, silt, etc.). Further, common operationalconditions (e.g., cold climates) may have the pumps subjected to thermalshock at start-up, which may utilize a specialized start-up procedure.Such challenges may result in significant limitations in conventionalpumps. For example, in a conventional pump, start-up processes may limittemperature ramp up to increments of 5° F. or less to prevent lockup dueto thermal shock. In addition, lockups and thermal shock incurred byconventional pumps may degrade the pump and lead to limited pump life(e.g., less than a month in some environments).

As an example, a glycol pump is often used in a glycol dehydrationsystem, where it may pump hot lean glycol into a glycol contactor, wherewater is stripped from the extracted natural gas. In this example, thelean glycol (e.g., substantially water fee, such as >99% purity) can befed into the top of a glycol contactor. The contactor is used to placethe glycol in contact with the “wet” natural gas; and through anabsorption process, the glycol strips the water from the “wet” naturalgas. The rich glycol (e.g., with the absorbed water) exits the contactorat the bottom, and the “dry” natural gas exits the contactor at the top.The rich glycol can be fed into a flash component and glycolregenerator, which removes hydrocarbons and water, resulting in leanglycol at an elevated temperature. The lean and hot glycol can then bepumped by the glycol pump back to the contactor. In one implementation,a heat exchanger may be used to reduce the temperature of the glycol,for example, down to a range of approximately 140-160 Deg. F. In oneaspect, an external (e.g., spur) gear pump may be designed that providesfor an extended pump life, and which can potentially handle thermalshock at startup. In one implementation, in this aspect, ways to addressthe challenges associated with this type of pump can include: hardeningof faces, such as using nitrocarburizing (e.g., Vitek), annealhardening, or thin dense chrome (e.g., Armoloy), or other; the use ofself-lubricating bushings (e.g., DU bushing); adjusting clearances tomitigate thermal shock; the use of thermal jacketing, or heating (e.g.,electrically) the pump to mitigate the thermal shock; the use of amechanical seal to improve sealing capability; the use of a thermalshock plate to allow for thermal shock; and/or the use of siliconcarbide bushings with a hardened or coated shaft to better handleabrasives. As one example, in this aspect, the pump technology describedherein can be used to pump hot Triethylene glycol (TEG) for natural gasdehydration. A long felt need in the market was identified by users ofsuch systems, used for pipeline injection, and with those involved innatural gas dehydration. Existing users of these systems are unhappywith current products available in the market, having including: shortpump life, sensitivity to thermal shock, temperature limits of existingpumps, and leakage issues.

In the following example implementations, individual component's thermalexpansion rates and material strengths were considered. Deliberateselection of materials that demonstrated controlled rates of the thermalexpansion. Further, innovative external gear pump improvements offersignificant advantages over conventional pumps. Such improvements mayinclude without limitation, for example, reduced leakage, increasedresistance to thermal shock and increased pump lifetimes in evenchallenging environments (e.g., on the order of years). Further,start-up processes may be increased from increments of 5° F. inconventional pumps to 100-150° F. or even eliminated.

There are several implementations described herein, which may be usedfor this type of application. In one or more of these implementations, amechanical seal can be used to mitigate leakage of the pumped fluid(e.g., hot TEG). Further, in one or more of these implementations, thematerials of construction used in the pump can be rated to 350 deg-F.,in order to meet the conditions of desired operation. As stated earlier,these designs may provide the following advantages, for example:increased pump life; simplified start-up with thermal shock; improvedperformance at extreme application temperatures; and more reliablesealing solution. The improved material of construction and internalcomponent clearances can also provide for operation that is morereliable and improved operational life.

In one implementation, a pump can be constructed using ductile iron fora base material, steel gears, self-lubricating bushings, and a hardenedsurface on the head and bracket. Further, in this implementation, tightend clearances on the shaft(s) can be used to increase theturn-up/turn-down ratio of the pump. In a further example, tightclearances may be the controlled running clearances between the gearsand other pump components. The amount of clearance designed into a pumpvaries depending on gear diameter and overall gear length. In aspecific, non-limiting example, a tight clearance may be about 1% whencomparing clearance to diameter (e.g., the running clearance on thegears may be controlled to a tolerance of <0.003″±0.0002″ for aparticular implementation). In further implementations, depending on thetechnology that is implemented, the running clearances can effectivelybe zero in a pressure-balance plate designed hydraulic positivedisplacement pump to about 0.125″ on a centrifugal pump. In otherimplementations, tolerances may be measured from the end of the gear tothe bracket of the housing and/or radially from the tips of the teeth ofthe gears to the housing. This feature may also allow the pump to runmore efficiently at operational temperature.

Adjustments may be made to either increase or decrease the runningclearance to better serve a particular application. But simplevariations may result in pumps with increased end clearance thatsacrifice efficiency and limit the overall ability to generate flow andovercome system pressures. In effect, such conventionally built pumpswill cease to function.

In another implementation, a pump can also be constructed using ductileiron for a base material, steel gears, self-lubricating bushings, and ahardened surface on the head and bracket. Further, additional runningclearance may be used at various portions (e.g., end clearance of thegears, and/or tips of the gears, shaft(s), etc.) to improve thermalshock performance, for example, by allowing for expansion andcontraction of some components during cold startup and operating attemperature.

Specifically, in an example glycol application (e.g., TEG), one obstacleis the potential of the pump to be subjected to large temperature spikesor thermal shocks. The rapid heating of the pump causes the internalcomponents to expand. Because the individual components are generallydifferent materials, they may expand at different rates and tightlycontrolled tolerances are eliminated which causes the pump to lock up.To counter this, the implementations described herein establish abalance of thermal shock capability while maintaining performance.Depending on the gear diameter and length, the amount of additional endclearance varies and may be an additional increase in a range of about15-25% additional spacing to balance thermal shock capability whilemaintaining performance. In a non-limiting example, a 15-25% increasemay be 0.0005″ to 0.001″ from a conventional pump. In otherimplementations, tolerances may be measured from the end of the gear tothe bracket of the housing and/or radially from the tips of the teeth ofthe gears to the housing.

In another implementation, the bracket and casing faces can be subjectedto increased hardening to improve the abrasive resistance of thesecomponents. As one example, the hardening may utilize a dense chromiumprocess for metals, such as Armoloy. In this implementation, the pumpcan also be constructed using ductile iron for a base material, steelgears, self-lubricating bushings, and a hardened surface on the head andbracket.

In another implementation, the pump can comprise a jacketing system thatallows the pump to be “warmed” prior to startup, for example, to makethe startup procedure easier. As an example, a jacketing system cancomprise thermal insulation, conduits used to distribute warming fluids,and/or electrical heating elements for warming the pump.

In another implementation, the pump can comprise a thermal shock plateproximate the cavity in the pump. As an example, the thermal shock platemay allow the pumping cavity to expand during thermal shock and shrinkduring steady state operation (e.g., at operational temperature). Thatis, a thermal shock plate, for example a variable end plate solution,may be configured such that conventional end clearances may be used inconjunction with the thermal shock plate allowing for the sudden thermalexpansion (of the gears for example) by providing a void for the plateto be pushed or expand into. As an example, the thermal shock plate maybe different than a typical pressure balance plate in that it may notforce itself against the gears with increasing differential pressure. Inone implementation, the thermal shock plate and mating components can bemachined to allow the thermal shock plate to expand and shrink thepumping cavity to a predetermined size, which may provide desiredrunning clearances for the gears and prolonging operational life of thepump.

FIGS. 1-4 are component diagrams illustrating various implementations ofpumps 100, 200, 300, 400, that may comprise one or more portions of oneor more systems described herein for pumping glycol. FIGS. 1A, 1B, and1C illustrate one implementation of a pump 100 in various views (front,side, cut-away). In this implementation, the pump 100 can comprise adriver shaft 102 and a driven shaft 104. As an example, the driver shaft102 can be coupled to (e.g., either directly or indirectly) some type ofprime mover (e.g., motor or the like) that applies rotary power to thedriver shaft 102, to rotate the shaft. In this example, the driven shaft104 rotates as a result of the rotation of the driver shaft 102, and theintermeshing of gears between the two shafts.

Further, the example pump 100 can comprise pump housing 106, housing theinternal workings of the pump 100; and a bracket and bushing assembly108. In one examples, an innovative bracket can be used to hold the sealholder, and for shaft support, and support of the bushings. For example,the same bracket can be utilized while a different seal can beintroduced for various application conditions. Further, utilizing thisinnovative bracket design, additional gear sections can be stacked witha longer drive shaft to add more bearings to support the shaft andmitigate and increase in loads on the bearings. This allows additionalgear sections to be added to increase flow rate, without increasing thesize (e.g., diameter) of the pump, which would occur in an existingsystem that merely increase the gear size. This allows for maintainingpressure ratings at an increased flow rate.

In FIGS. 1A, 1B, and 1C, the example pump 100 can comprise a gearassembly 110. The gear assembly 110 can comprise a series of gears, suchas a first gear 112 and a second gear 114, respectively coupled to theirassociated shafts 102, 104. For example, the gears 112, 114 can bearranged in an intermeshing disposition with each other. In thisexample, rotation of the driver shaft 102 results in rotation of thefirst gear 112, which results in rotation of the second gear 114 and thedriven shaft 104. As an example, the rotation of the intermeshing gearscreate expanding volume on the inlet side of the pump, and liquid flowsinto the internal pump cavity 120 and is trapped by the gear teeth asthey rotate. As the liquid travels around the internal pump cavity 120in the pockets between the teeth and the walls of the cavity, themeshing of the gears forces liquid through the outlet port.

Additionally, the example pump 100 can comprise a seal 116. For example,the seal 116 may be used mitigate leakage of fluid from the internalpump cavity 120 to outside of the pump, such as using some type ofmechanical seal. The example pump 100 can comprise a head and bushingassembly 118. As an example, an innovative head design may allow theheads to be rotated without changing the bracket and casings. Forexample, this allows a user to rotate the head to provide for eitherclockwise (CW) or counter-clockwise (CCW) rotation in the same pump.Visual indicators may be provided to allow the user to set up the pumpin the desired CW or CCW rotation. Further, this innovative designallows the designer of the pump installation to place the pump system inan appropriate position for the site situation. For example, the usercan merely disassemble the pump and set the way that is appropriate forthe situation, without replacing additional parts in the pump.

Further, in one aspect, an innovative bracket design may allow formultiple mechanical seal options with a single bracket, which can allowend users to choose between a standard component seal, a balancedcomponent seal, or a cartridge seal with provisions for leak detectionsystems. Additionally, in this aspect, gear sections can be added to thepump to increase the flow rate while maintaining the original pressurerating. For example, being able to add gear sections is like having two,three or more pumps, but with only one seal and one prime mover.Machining on the separation plates and heads can also be provided toallow for the same parts to be flipped to achieve a CW or CCW build.

In another example, the innovative bracket can be used to hold the sealholder, and for shaft support. For example, the same bracket can beutilized while a different seal can be introduced for variousapplication conditions. Further, utilizing this innovative bracketdesign, additional gear sections can be stacked with a longer driveshaft to add more bearings to support the shaft and mitigate an increasein loads on the bearings. This allows additional gear sections to beadded to increase flow rate, without increasing the size (e.g.,diameter) of the pump, which would occur in an existing system thatmerely increase the gear size. This allows for maintaining pressureratings at increased flow rates.

As one example, as illustrated in the implementation of the pump 100,tighter clearances may be utilized. In this example, the tighterinternal component clearances may allow for improved function for theoperation, and can also provide for operation that is more reliable andimproved operational life. In one example, the tighter clearances may beprovided at the end of the gear(s), such as between the gear end(s) andthe head assembly 118, and/or between the gears 112, 114 and the casing110. This may be used to increase the turn-up/turn-down ratio of thepump.

The example pump system can comprise improved material construction thatprovides for improved operation, less maintenance, longer operationallife, and lower overall cost. For example, the improved materials cancomprise harder gears and gear teeth, such as hardened steel, steelalloys, and other metals that resist abrasion and other damage. In oneimplementation, one or more components can be Vitek hardened to increasewear resistance. By way of nonlimiting example, one of the improvedmaterials may be a powdered metal described in standard FN-0208-155HTfrom MPIF Standard 35. In another non-limiting implementation, theimproved material may be an alloy steel comprising an AISI 8620 basematerial with a carbon nitrated heat-treated steel layer over the basematerial. Further, the pump parts, including the gears, gear teeth,heads, casings, drive shaft, seal, bearings, and bushings can be formedwith tighter tolerances (e.g., gaps) than previously found in thesetypes of pumps. The improved tolerances and materials can help provideimproved pressure ratings, improved use with non-lubricating fluids, andimproved overall operational life.

FIGS. 2A, 2B, and 2C illustrate another implementation of a pump 200 invarious views (front, side, cut-away). In this implementation, theexample pump 200 can also comprise the various components illustratedand identified in FIG. 1, including: the driver shaft; driven shaft;pump housing; bracket and bushing assembly; gear assembly; 1^(st) and2^(nd) gears; seal; head and bushing assembly, and internal pump cavity.Further, in this implementation, the example pump 200 can comprise aseparation plate with a jacketed head assembly 222. As illustrated, theseparation plate 222 can be disposed between the bracket and bushingassembly and a head assembly. In one example, the separation plate witha jacketed head assembly 222 may be used to provide pre-startup warmingto mitigate thermal shock associated with use of the pump in coldconditions.

FIGS. 3A, 3B, and 3C illustrate another implementation of a pump 300 invarious views (front, side, cut-away). In this implementation, theexample pump 300 can also comprise a thermal shock plate 330. Forexample, the thermal shock plate 330 can be placed next to the internalpump cavity (e.g., 120). In this example, the thermal shock plate 330may allow the pumping cavity to expand during thermal shock and shrinkto a predetermined size during steady state operation (e.g., atoperational temperature). In this way, the effects of thermal shock onthe operation of the pump can be mitigated.

FIGS. 4A, 4B, and 4C illustrate another implementation of a pump 400 invarious views (front, side, cut-away). In this implementation, theexample pump 400 can also comprise additional clearance 440. As anexample, the additional clearance can also help mitigate thermal shock,as it can provide additional room for expansion or contraction of thecomponents of the pump. Further, the example pump 400 can comprise afoot 450, which may be used to secure the pump 400 to a set position,such as in a glycol dehydration system.

The word “exemplary” is used herein to mean serving as an example,instance or illustration. Any aspect or design described herein as“exemplary” is not necessarily to be construed as advantageous overother aspects or designs. Rather, use of the word exemplary is intendedto present concepts in a concrete fashion. As used in this application,the term “or” is intended to mean an inclusive “or” rather than anexclusive “or.” That is, unless specified otherwise, or clear fromcontext, “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, if X employs A; X employs B; or Xemploys both A and B, then “X employs A or B” is satisfied under any ofthe foregoing instances. Further, At least one of A and B and/or thelike generally means A or B or both A and B. In addition, the articles“a” and “an” as used in this application and the appended claims maygenerally be construed to mean “one or more” unless specified otherwiseor clear from context to be directed to a singular form.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary implementations of thedisclosure. In addition, while a particular feature of the disclosuremay have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. Furthermore, to the extent thatthe terms “includes,” “having,” “has,” “with,” or variants thereof areused in either the detailed description or the claims, such terms areintended to be inclusive in a manner similar to the term “comprising.”

The implementations have been described, hereinabove. It will beapparent to those skilled in the art that the above methods andapparatuses may incorporate changes and modifications without departingfrom the general scope of this invention. It is intended to include allsuch modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A pump for pumping non-lubricating fluids,comprising: an internal pump chamber comprising a first material; adriver shaft that provides rotational power to the pump; a driven shaftthat rotates as a result of the rotational power from the driver shaft;a first external gear disposed on the driver shaft in the internal pumpchamber, the first external gear comprising a second material; a secondexternal gear disposed on the driven shaft in the internal pump chamber,the second external gear comprising the second material, the first gearand the second gear being disposed in an intermeshing engagement thatdrives fluid through the internal pump chamber under the rotationalpower; and a head assembly disposed at an end of the driver shaft andthe driven shaft; wherein the first material is different than thesecond material, and the first material and the second material arerated to 350° F. and are resistant to thermal shock.
 2. The pump ofclaim 1, wherein the fluid comprises glycol.
 3. The pump of claim 1,wherein the first material comprises ductile iron and the secondmaterial comprises steel, hardened steel, or a steel alloy.
 4. The pumpof claim 1, further comprising self-lubricating bushings operablyconnected to the driver shaft and the driven shaft.
 5. The pump of claim1, further comprising a bracket assembly disposed at an opposite end ofthe driver shaft and the driven shaft from the head assembly.
 6. Thepump of claim 5, wherein the head assembly and the bracket assemblycomprise a hardened surface layer, the hardened surface layer beingrated to 350° F. and resistant to thermal shock.
 7. The pump of claim 6,wherein the hardened surface comprises a surface hardened by a densechromium process.
 8. The pump of claim 1, comprising a thermal shockplate disposed adjacent the internal pump chamber that allows theinternal pump chamber to expand and contract to mitigate thermal shockat startup, the thermal shock plate being rated to 350° F. and resistantto thermal shock.
 9. The pump of claim 1, comprising a clearance betweenthe end of the driver shaft and the head assembly, and between the endof the driven shaft and the head assembly, each respective clearanceconfigured such that the end of the driver shaft and the head assemblyand the end of the driven shaft and the head assembly are substantiallysealed from leakage.
 10. A pump for pumping non-lubricating fluids,comprising: an internal pump chamber; a driver shaft that providesrotational power to the pump; a driven shaft that rotates as a result ofthe rotational power from the driver shaft; a first external geardisposed on the driver shaft in the internal pump chamber; a secondexternal gear disposed on the driven shaft in the internal pump chamber,the first gear and the second gear being disposed in an intermeshingengagement that drives fluid through the internal pump chamber under therotational power; a head assembly disposed at an end of the first shaftand second shaft; and a thermal shock plate disposed adjacent theinternal pump chamber that allows the internal pump chamber to expandand contract to mitigate thermal shock at startup, the thermal shockplate being rated to 350° F. and resistant to thermal shock.
 11. Thepump of claim 10, wherein: the internal pump chamber comprises a firstmaterial; and the first external gear and the second external gear eachcomprise a second material, the first material being different than thesecond material, and the first material and the second material beingrated to 350° F. and are resistant to thermal shock.
 12. The pump ofclaim 11, wherein the first material comprises ductile iron and thesecond material comprises steel, hardened steel, or a steel alloy. 13.The pump of claim 11, further comprising a bracket assembly disposed atan opposite end of the first shaft and the second shaft from the headassembly.
 14. The pump of claim 13, wherein the head assembly and thebracket assembly comprise a hardened surface layer, the hardened surfacelayer being rated to 350° F. and resistant to thermal shock.
 15. A pumpfor pumping non-lubricating fluids, comprising: an internal pumpchamber; a driver shaft that provides rotational power to the pump; adriven shaft that rotates as a result of the rotational power from thedriver shaft; a first external gear disposed on the driver shaft in theinternal pump chamber; a second external gear disposed on the drivenshaft in the internal pump chamber, the first gear and the second gearbeing disposed in an intermeshing engagement that drives fluid throughthe internal pump chamber under the rotational power; a head assemblydisposed at an end of the first shaft and second shaft; and an area ofadditional clearance between the end of the driver shaft and the headassembly, and between the end of the driven shaft and the head assemblyconfigured such that the additional clearance absorbs thermal shock atstartup of the pump.
 16. The pump of claim 15, further comprising abracket assembly disposed at an opposite end of the first shaft and thesecond shaft from the head assembly.
 17. The pump of claim 16, whereinthe head assembly and the bracket assembly comprise a hardened surfacelayer, the hardened surface layer being rated to 350° F. and resistantto thermal shock.
 18. The pump of claim 15, wherein: the internal pumpchamber comprises a first material; and the first external gear and thesecond external gear each comprise a second material, the first materialbeing different than the second material, and the first material and thesecond material are rated to 350° F. and are resistant to thermal shock.19. The pump of claim 18, wherein the first material comprises ductileiron and the second material comprises steel, hardened steel, or a steelalloy.
 20. The pump of claim 15, further comprising a thermal shockplate disposed adjacent the internal pump chamber that allows theinternal pump chamber to expand and contract to mitigate thermal shockat startup, the thermal shock plate being rated to 350° F. and resistantto thermal shock.